A "Free Electron Laser" for wavelengths down to 6 nm in the vacuum-ultraviolet and soft X-ray regime (VUV FEL) is under construction at the TESLA Test Facility (TTF) at DESY. It is operated in the "self-amplified spontaneous emission" (SASE) mode and delivers sub-picosecond radiation pulses, with gigawatt peak powers.

The demands on high beam quality impose stringent requirements on the Low Level Radio Frequency (LLRF) control for the 48 superconducting cavities and the normalconducting RF Gun. The RF system is operated in pulsed mode and up to 32 cavities are driven by one klystron. In order to achieve a field stabiliy of 3e-4 for gradient and about 0.1 deg. for phase in presence of severe Lorentz force detuning, microphonics and heavy beamloading, new concepts have been developed.


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